Balanced IR\nNonlinear Optical Performance Achieved\nby Cation–Anion Module Cosubstitution in V‑Based Salt-Inclusion\nOxychalcogenides

Oxychalcogenides have become notable contenders for infrared\nnonlinear\noptical (IR NLO) applications because of their diverse heteroanionic\nfunctional motifs. However, while the main group elements are well-explored\nfor these motifs, transition elements have been less studied and lack\nhigh-performance materials. To address this gap, we investigated a\nseries of noncentrosymmetric [Ba<sub>4</sub>(Ba<sub>6</sub>S)][(VO<sub><i>x</i></sub>S<sub>4–<i>x</i></sub>)<sub>6</sub>] (space group: <i>P</i>6<sub>3</sub>), the first\nV-based salt-inclusion oxychalcogenides demonstrating phase-matched\nIR-NLO properties. We achieved this by cation–anion module\ncosubstitution in the centrosymmetric structure of [Ba<sub>4</sub>(Ba<sub>6</sub>Cl<sub>2</sub>)][(VO<sub>4</sub>)<sub>6</sub>] (space\ngroup: <i>P</i>6<sub>3</sub>/<i>m</i>). The novel\n[Ba<sub>4</sub>(Ba<sub>6</sub>S)][(VO<sub><i>x</i></sub>S<sub>4–<i>x</i></sub>)<sub>6</sub>] features isolated\nheteroanionic [VO<sub><i>x</i></sub>S<sub>4–<i>x</i></sub>]<sup>3–</sup> units, charge-balanced Ba<sup>2+</sup> cations, and a one-dimensional cationic chain of [Ba<sub>6</sub>S]<sup>10+</sup> octahedral units. Moreover, [Ba<sub>4</sub>(Ba<sub>6</sub>S)][(VO<sub>3</sub>S)<sub>6</sub>] exhibits notable\nproperties including a high second-harmonic-generation intensity (1.33\n× AgGaS<sub>2</sub>@2900 nm), a substantial laser-induced damage\nthreshold (7.65 × AgGaS<sub>2</sub>), a broad IR cutoff edge\n(up to 11.2 μm), and significant birefringence for phase matching\n(Δ<i>n</i> = 0.073@2900 nm). Structural analysis and\nDFT calculations demonstrate that the configuration of the [VO<sub>3</sub>S]<sup>3–</sup> units enhances NLO properties and increases\nstructural anisotropy. Our findings suggest that V-based salt-inclusion\noxychalcogenides are a promising class for IR-NLO applications and\nhighlight cation–anion module cosubstitution as an effective\napproach for creating high-performance heteroanionic NLO crystals.